Attapulgite dispersions in water at 25 to 30% clay solids predispersed with TSPP (approximately 2-3% tetrasodium pyrophosphate based on the clay weight) are available from commercial sources and can be made in situ by the user. Processing in either case consists of dissolving the TSPP dispersant in water, adding the clay while agitating and continuing agitation until the major portion of the clay is dispersed. The dispersion can be used as made or can be processed to remove undispersed impurities. Other chemical agents such as small amounts of NaOH can be included as functional additives in the dispersion. They are added either before or after the incorporation of the clay.
The dispersion of attapulgite clay at 25 to 30% solids in water using condensed phosphates as dispersing agents is an old and well-known practice and has been described many times in the literature. The technique has also been described as a step in many U.S. Patents where the inventive feature has been some further treatment of the dispersion. U.S. Pat. Nos. 3,050,863, 3,509,066 and the references cited therein describe some methods of further treatment as examples.
When colloidal grades of attapulgite are used as gelling agents to stabilize suspensions or to thicken an undesirably thin aqueous system, the user often has the option as to how he will incorporate the clay into his system. He may either add the dry clay during processing and disperse it by mechanical work input or he may add predispersed clay which has been subjected to prior processing as described above. In either case the clay must end up with an extended flocculated structure in the final product to give the desired thickening or suspension effects.
The advantages of using predispersed attapulgite are that (1) the clumps of needles present in the dry colloidal clay products can be dispersed in water using a condensed phosphate dispersant with much less work input than is necessary in mechanical dispersion and (2) the efficiency of the predispersed clay in its intended use is 2 to 3 times better than that achieved in strictly mechanical dispersion. The disadvantages of predispersed clay slurries are (1) the poor economics of shipping 75% water for long-distance trips and (2) the fact that the freezing point of the dispersion is approximately 32.degree. F. This second factor, the 32.degree. F. freezing point, prevents the shipment and outdoor storage of predispersed slurries in many parts of the U.S. during the winter. In many parts of the country this would prevent shipment in unheated tank cars and trucks from October of one year to April of the next year. This situation has been a retarding factor in the development and use of such a desirable product.
Materials normally used as antifreezes, such as methanol, ethanol, isopropanol, ethylene glycol, propylene glycol and eutectic salt solutions, cannot be used in the above-described predispersions because they cause the predispersion to flocculate and become excessively viscous so that it can no longer be stirred or pumped. Furthermore, after such a flocculation it no longer exhibits the above-mentioned ease of use and must be redispersed mechanically for utilization.